1. Field of the Invention
The invention relates to devices displaying and holding the speed of the vehicle and relating this speed to the fuel consumption; in particular the described invention concerns a method and device for measuring and holding the economic speed of the engine and vehicle.
2. State of the Prior Art
There are described in the patent literature, and are in use numerous, recently predominantly computerized devices, measuring fuel consumption and cruise control arrangements holding the road speed of the vehicle. The instantaneous and/or average fuel consumption per mile is measured (e.g. U.S. Pat. Nos. 4,205,376; 4,205,377; 4,403,584; 4,437,445) with additionally calculated information such as range of fuel consumption, remaining fuel in the tank etc.
The devices of cruise control (e.g. U.S. Pat. Nos. 4,138,723; 4,196,787; 4,453,517; 4,505,357; 4,516,652; 4,519,469) are set by the driver on desired speed of the vehicle. However, both types of devices are not directly related to the economic speed of the vehicle. Therefore, up to date there is no such instrument which unequivocally and universally relates the speed of the vehicle to fuel consumption by indicating and holding the economic speed of the vehicle.
Instantaneous speed and fuel consumption of the vehicle are influenced among others by load, road and weather conditions. Knowing an instant, average and range of fuel consumption does not mean that driver is actually able to use such devices in order to drive a vehicle at the economic speed.
Non-linear characteristics of the engine performance such as brake horsepower, torque and specific fuel consumption versus engine speed undergo changes depending the load and road conditions, but their shape remains the same. Therefore, to use the economic speed of the engine and vehicle means to follow at least one of these characteristics and hold the actual speed around the extreme point of such characteristics. The point and range of the economic speed of the engine and vehicle should be used to find automatically the economic speed: both geared speed and travelling velocity of the vehicle.
From the fuel consumption curve is evident that for a particular point on the operating range of the engine performance, the fuel consumption is minimum and the power developed by the engine is maximum. For continous operation, the selection of the economic operating speed results in large savings in fuel, maintainance and repair costs.
The major engine builders have developed a new "high torque concept", which provides increased performance and better fuel economy. It is also known that in order to execute a smooth gear shift and pick up sufficient power to accelerate the vehicle, the rpm must not fall below the maximum torque range.
Therefore, the method of estimation of the point of the econmic speed of the engine and vehicle is based upon constant finding the function of fuel consumption F to the torque T EQU f.sub.t =F/T,
or the function of fuel consumption to the vehicle velocity V EQU f.sub.v =F/V
with subsequent time-quantization and differentiation. The derivative of the quantitized impulses of such ratio Q versus engine speed gives a respective function EQU f=dQ/dt,
which is further tested for estimation of the sign of the derivative and checking the point of its change in order to find the point of minimum of the function, i.e. the point of maximum of the economic speed.
The invention has three objects:
to find a point of the point and range of the economic speed and to monitor any deviations from it during operation of the engine and vehicle; PA1 to couple the point of maximum of the economic speed with the optimal moment for switching the gears, and PA1 to use this point for control and holding the economic speed of the engine and vehicle.
The above will be apparent from the description of the prefered embodiment accompanied by the following drawings.